1. Field of the Invention
The present invention relates to print media detection, and, more particularly, to a method of media type differentiation, such as distinguishing between high glossy media and transparency media, in an imaging apparatus.
2. Description of the Related Art
Various attempts have been made to try to sense when paper is being processed through a printer. One such attempt distinguishes between the presence and absence of paper by providing a high contrast ratio sensor including a light emitter and a pair of photodetectors functioning as a diffuse detector and a reflective detector. The two photodetectors are connected in a manner to cause the diffuse detector output to subtract from the reflective (or transmissive) detector output. This subtraction of signals provides a high contrast ratio. The pair of photodetectors may be located on the same side of the print medium as the light emitter, and a mirror may be positioned on the opposite side of the paper to aid in detecting the presence of the sheet of paper.
More recently, media sensors have been used to detect the type of media in an imaging device, such as an ink jet printer, by optically measuring the glossiness of the media using a media sensor detecting each of specularly reflected light and diffusely scattered light. To measure the glossiness, a collimated beam of light is directed towards the media and a reflectance ratio (R) of the detected reflected specular light intensity and the detected diffusively scattered light intensity is calculated. The media sensor is initially calibrated by measuring a reflectance ratio (R0) on a known gloss media. A normalized reflectance ratio (Rn) is calculated using the formula: Rn=(R/R0). Normalized reflectance ratio Rn then is used to identify the media type of an unknown media by a comparison of the normalized reflectance ratio Rn to a plurality of normalized reflectance ratio Rn ranges, each range being associated with a particular type of media. For example, if the media sensor is calibrated with a perfectly diffuse media, then the normalized reflectance ratio Rn ranges might be established as in the following table.
TABLE 1Media Determination Based on NormalizedReflectance Ratio RnRn RangeMedia TypeRn < 1.5Coated Paper1.5 ≦ Rn < 3Plain Paper3 ≦ Rn < 10Photo Paper10 ≦ RnTransparency
In practice, however, it may be quite difficult using the normalized reflectance ratio range approach to distinguish between a high glossy media sheet, such as a high gloss photo paper, and a transparency media sheet. Further, the normalized reflectance ratio approach requires both a specular detector and a diffuse detector.
What is needed in the art is an improved media sensing apparatus that can reliably distinguish between high glossy media and transparency media.